Implementation of 'Andrew's Monotone Chain Algorithm' for convex hull construction.

Andrew, A.M. (1979): Another Efficient Algorithm for Convex Hulls in Two Dimensions. Info. Proc. Letters 9, pp.216-219.

Sunday, D. (2001-2006): The Convex Hull of a 2D Point Set or Polygon. Geometry Algorithms Home. (Web site with source code)

The Algorithmist (9 November 2011): Monotone Chain Convex Hull. (source code)

Name	Type	Identifier	Description	Constraints
Input
Points	shapes, input	SHAPES
Output
Convex Hull	shapes, output	HULLS
Minimum Bounding Box	shapes, output, optional	BOXES
Options
Object Identifier	table field	FIELD
Hull Construction	choice	POLYPOINTS	This option does not apply to simple point layers.	Available Choices: [0] one hull for all shapes [1] one hull per shape [2] one hull per shape part Default: 1
Polygon Convexity	boolean	POLYGONCVX	Describes a polygon's compactness as ratio of its area to its hull's area.	Default: 0